In electrical power distribution, a bus bar is a stripe on bar of copper brass or aluminium that conducts electricity within a switch board, distribution board, substation battery bank or other electrical Apparatus,. its main purpose is to conduct electricity. the cross sectional size of the busbar determines the maximum amount of current that can be safely Carried. A bus duct is a metal bar that supports and contains a group of ELECTRICAL bus bars. that duct comes in standard 10 foot lengths. the greatest advantages of bus ducts is that they are capable of adding or removing a branch circuit without removing voltage from the whole duct.